High-frequency ultrasound biomicroscopy (UBM) provides high-resolution cross-sectional images of anterior segment structures. Few published reports have correlated abnormal UBM images with histopathologic findings. A recent report by Marigo et al1 compared ultrasound images of iris and ciliary body melanomas with their histopathologic features. They found that UBM accurately defined the tumor shape andthe extent of local invasion. There is histopathologic evidence that iris melanomas can spread through unguarded (Scheie procedure2 and iridencleisis3) and guarded (trabeculectomy4) glaucoma procedures. We show that UBM can accurately determine the depth of tissue penetration by an iris melanoma into a trabeculectomy site by correlating the clinical images with the histopathologic features after enucleation.

Report of a Case

In January 1995, a 59-year-old white woman was evaluated for rising intraocular pressure in the left eye. The patient had been prescribed timolol maleate, pilocarpine, apraclonidine hydrochloride, andacetazolamide by the referring ophthalmologist. She had a history of a pigmented iris tumor in the left eye that had been stable for many years.

On examination, visual acuity was 20/20 OD and 20/30 OS. Applanation pressure was 15 mmHg OD and 49 mmHg OS. Results of slitlamp and gonioscopic examinations of the right eye were normal. The trabecular meshwork had minimal pigmentation. In the left eye, a slightly elevated pigmented lesion was visible in the peripheral iris between the 2- and 3-o'clock positions. Transillumination did not show involvement of the ciliary body. The angle was open, but clumps of pigment were layered in the inferior angle, and the entire trabecular meshwork was darkly pigmented. Results of a retinal examination in each eye were normal.

It was recognized that this iris lesion most likely was a malignant melanoma, but after extensive discussion, the patient chose to have a trabeculectomy to control intraocular pressure and preserve vision rather than undergo an immediate enucleation. The procedure was performed without complication. The postoperative course was uneventful, and intraocular pressure was reduced to 10 to 12 mmHg without medications (Figure 1A).

A, A postoperative slitlamp photograph of the left eye shows a localized pigmented iris lesion between the 2- and 3-o'clock positions, a peripheral iridectomy at the 11:30-o'clock position, and a filtration bleb in the superonasal quadrant. B, Eleven months later, there is diffuse involvement of the iris and pigment in the filtration bleb.

The left eye continued to do well, with a visual acuity of 20/20 and an intraocular pressure of less than 20 mmHg, until April 1996. At that time, the patient sought treatment for a 3-day history of eye pain; intraocular pressure was 32 mmHg OS. Slitlamp examination showed patchy pigmentation over the entire iris surface and within the bleb cavity (Figure 1B). High-frequency UBM of the bleb and adjacent structures was performed with an Ultrasound Biomicroscope Model 840 (Zeiss Humphrey Systems, Dublin, Calif). This instrument hasa frequency of 50 MHz and a lateral and axial resolution of 50 µm. The penetration depth is 5 mm. It scans at a rate of 8 Hz with a sampling resolution of 5 µm. Ultrasound biomicroscopy showed evidence of tumor proliferation within the sclerectomy and filtration bleb (Figure 2). The eye was enucleated. Results of a metastatic workup, including a chest radiograph, liver function tests, and a computed axial tomographic scan of the abdomen and pelvis, were normal. Seven years later, the patient was in good health and without evidence of metastatic disease.

High-frequency ultrasonography cross-sections through the filtration bleb (open arrows) and sclerectomy (closed arrow) show cellular material within the bleb (asterisk). The iris root and ciliary body appear normal, but the wall of the bleb is thickened.

Pathologic Description

Gross examination of the enucleated specimen showed a 23 × 23× 25-mm left eye with 8.0 mm of optic nerve attached. A bleb in the superonasal quadrant measured 10 × 6 mm and an iris defect was present at the 11:30-o'clock position. A pigmented tumor arose from the peripheral iris andextended into the angle. Histopathologic analysis showed a diffuse melanoma of the iris that was predominately composed of spindle B cellsbut with a moderate number of epithelioid cells. Tumor infiltrated the trabecular meshwork, filtering bleb, and sclera adjacent to the operative site (Figure 3). There was seeding into the anterior chamber, on the trabecular meshwork, onto the anterior and posterior lens capsule and suspensory ligaments, and over the inferior pars plana. No extrascleral or extraconjunctival extension was seen. The optic nerve showed glaucomatous cupping with cavernous degeneration posterior to the lamina cribosa.

A cross-section through a filtration bleb (open arrow) and sclerectomy (closed straight arrow) shows cellular infiltration of the bleb wall, the edge of the sclerectomy, the iris root, the adjacent sclera (curved arrows), and within the bleb cavity (asterisk) (hematoxylin-eosin, original magnification ×40). Note the similarity to features shown by high-frequency ultrasonography in Figure 2A.

Comment

Iris melanomas are uncommon. In general, they grow slowly, and patients have an excellent prognosis because of their low metastatic potential (<5%).5- 7 It is difficult to decide what course of action is appropriate when a pigmented iris lesion grows because benign and malignant lesions canenlarge and spread into adjacent structures. Both can cause elevated intraocular pressure. Because iris melanomas are more likely to metastasize if there is involvement of the iris root or angle with elevated intraocular pressure or when there is extraocular spread, it would be helpful to have a noninvasive clinical tool to help guide management decisions. In our case, it was remarkable how closely the findings from UBM mirrored the findings demonstrated by low-power microscopy of the fixed tissue. This study and others1,8 show the utility of high-frequency UBM in providing useful information about tumor morphology, growth pattern, and depth of penetration.